The present invention relates to an apparatus which melts and extrudes synthetic resin materials.
Generally, synthetic resin compounds, prepared by mixing great quantities (for example, equivalent to a resin) of extenders such as gypsum or calcium carbonate in thermoplastic resin such as polyethylene, or polypropyrene are incombustible or produce less noxious gas even when these compounds burn and therefore the compounds are widely used as various types of molded products, packing materials and architechtural materials. Furthermore, the resin can be saved by using the materials in this type of composition and the demands for these synthetic resin compounds will increase in the future.
In case of producing the pellets of synthetic resin compounds which are thus greatly extended, the thermoplastic resin and extenders should be kneaded while being melted and the mixture should be homogenized.
If the kneading efficiency of the extruder is low, great quantities of extender cannot be added, the compound cannot be homogenized and the producing speed becomes slow.
The principal object of the present invention is to provide an extruder capable of highly efficient kneading of the resin compounds, in view of the problems described above.
This principal object can be applied to the cases other than production of extended resin compounds. That is, it is applied to production of a compounded resin by mixing a plurality of different kinds of resin materials and production of bonding agents and paints by blending the resin and specific materials.
With respect to the bonding agents, since the conventional solvent-type, emulsion-type or water-soluble bonding agents provides its adhering force to objective materials through evaporation of a medium and drying and solidifying of the bonding agent, the industrial use of this type of the bonding agent is confronted with various problems such as the necessity of large-capacity drying equipment, deterioration of the productivity and environmental pollution and danger of fire due to production of a great volume of solvent vapor when the solvent type bonding agent is dried.
Instead of using bonding agents with the accompanying various problems, the hot-melt type bonding agents have recently been developed and their use is spreading.
This hot-melt type bonding agent is a solid bonding material containing no water or solvent and readily becomes a low-viscosity fluid when it is heated.
When this hot-melt type bonding agent is used, it is melted to a fluid by heating and applied to objective materials, and the materials are instantaneously bonded after spontaneous cooling.
Accordingly, the hot-melt type bonding agent requires a shorter time for the bonding work than other bonding agents for which the drying equipment is required, and this bonding agent is economical because the drying equipment is unnecessary and therefore provides high productivity and does not produce a solvent vapor as in case of a solvent type bonding agent. Thus it is forecast that the demands for the hot-melt type bonding agent will increase more and more in the future.
The blending of materials for the hot-melt type bonding agent can be varied in accordance with the applications. Generally it contains the base polymer (for example, EVA, polyethylene with low molecular weight, APP, polyisobutylene, styrenebutadiene, etc.) as the principal component, viscous resin (for example, rosin, terpene resins, petrochemical resins, cumarone, indene resins, etc.), various waxes and stabilizing agent.
As described above, a blended resin compound of an extremely low viscosity (viscosity: 100 .about. 100,000 cps) when it is melted as compared with general thermoplastic resins (usual viscosity: 1,000,000 cps or over) can be widely used for other applications such as, for example, coating, painting, printing, etc. in addition to the bonding applications, and the blended resin compounds can be integrally referred to as the hot-melt materials.
In general, hot-melt materials are supplied to users in the form of pellets, biscuits or small blocks; however, it is difficult to mold the hot-melt material by the extruders for general plastic materials for its specific characteristic, that is, extremely low viscosity when it is melted.
When an extruder for general plastic materials is used to extrude the hot-melt material, the molten hot-melt material has a small low friction with the internal surface of the extrusion cylinder, the hot-melt slips and the extrusion screw cannot perform conveying function of the hot-melt material.
Therefore, a complicated expensive plant as shown in FIG. 16 is operated for melting and processing the conventional hot-melt materials. In FIG. 16, raw materials of the hot-melt material are melted in the melting tank T1 and T2 and the molten hot-melt material is sent to the third tank T3 through the valves and the flow passage A1 shown with solid lines in the figure. In the third tank T3, the temperature of the molten material is adjusted and the mixing is more promoted. The first melting tank T1 and the second melting tank T2 are provided to perform continuously the operation by melting and stirring the material in one melting tank while the molten material is being discharged from the other tank. The molten material discharged from the third tank T3 is filtered by the strainer S1 or S2 and is sent under pressure to attachment AT such as the T dies by the pump P with internally rotating gears, whereby the molded products are obtained. In this case, strainers S1 and S2 are properly changed over in accordance with their filtering conditions.
In a plant like this, the melting tanks, strainers and pump should be heated to maintain the temperature of the molten material at a certain specified temperature. For this purpose, the heating medium boiler B and feeder F should be installed to form the pipe passage of the heating medium as shown with broken line A2 in the figure, flow passage A1 for the molten material should be made by dual piping and heated by said heating medium and many valves and cocks should be provided in the piping. In addition, the cooling water piping is required for the pump.
As described above, the conventional plants have been complicated and expensive in their constructions. In actual operation, these plants are disadvantageous in that it takes long until the material is melted and the hot-melt material should be completely discharged from all the pipings after extruding operation.
Furthermore, the pump type machines cannot process the hot-melt material of high viscosity (100,000 cps or over) for which the demands are expected to increase.
Another object of the present invention is to supply an extruder which is capable of extruding a hot-melt material as described above likewise general extruding machines and to vastly improve the efficiency and economy in melting and molding operations of the hot-melt material.
Further another object of the present invention is calrified in the detailed description of the construction based on the drawings.